Move paint code for RenderScrollbar and RenderScrollbarPart into ScrollbarPainter.

Source/core/rendering/RenderScrollbar.h

Index: Source/core/rendering/RenderScrollbar.h
diff --git a/Source/core/rendering/RenderScrollbar.h b/Source/core/rendering/RenderScrollbar.h
index 99b609bed51aafdb3095a4649eb83c571a65b3a5..fccf926b78394f5b33ad660687756cd46d3d2811 100644
--- a/Source/core/rendering/RenderScrollbar.h
+++ b/Source/core/rendering/RenderScrollbar.h
@@ -49,8 +49,6 @@ public:
 
     RenderBox* owningRenderer() const;
 
-    void paintPart(GraphicsContext*, ScrollbarPart, const IntRect&);
-
     IntRect buttonRect(ScrollbarPart);
     IntRect trackRect(int startLength, int endLength);
     IntRect trackPieceRectWithMargins(ScrollbarPart, const IntRect&);
@@ -59,6 +57,8 @@ public:
 
     virtual bool isOverlayScrollbar() const OVERRIDE { return false; }
 
+    RenderScrollbarPart* getPart(ScrollbarPart partType) { return m_parts.get(partType); }
+
 private:
     virtual void setParent(Widget*) OVERRIDE;
     virtual void setEnabled(bool) OVERRIDE;